1. Field of the Invention
The present invention relates to electrical transformers and more particularly to high power, high density electrical transformers.
2. Description of the Related Art
As is known in the art, electrical transformers have a wide variety of applications. The transformer includes a magnetic core, a primary winding and an adjacent secondary winding each associated with the magnetic core. A primary electrical current passing through the primary winding induces a corresponding magnetic field around the primary winding. The magnetic field is coupled into the magnetic core by induction. The magnetic field flowing through the magnetic core induces a secondary current to flow through the secondary winding. The ratio of the number of secondary turns to the number of primary turns determines the transform of primary voltage in to secondary voltage out.
As is also known in the art, it is desirable to reduce the size of electrical transformers. One example of an electrical transformer having a reduced size is disclosed in U.S. Pat. No. 6,952,153 by Jacobson et al., issued on Oct. 4, 2005 and entitled ELECTRICAL TRANSFORMER. In the example of the '153 patent, a pair of opposing multilayer printed circuit or wire boards (PCB or PCW) are separated by a dielectric spacer having a central aperture passing between the PCB's. A core assembly installs into the central aperture and is embedded between the opposing PCB's. The core assembly includes a magnetic core formed with core apertures passing between the PCB's. The core assembly also includes vertical conductors that electrically interface with each of the PCB's at a plurality of solder joints. The transformer windings include horizontal conductors incorporated as conductive paths in each of the PCB's and the vertical conductors incorporated within the core assembly.
While the embedded core transformer assembly disclosed in the '153 patent reduces the volume and weight of a transformer by incorporating portions of the transformer windings within the multilayered PCB's, conventional embedded core transformers have drawbacks. In particular, conventional embedded core transformers include a large number of solder joints between the core assembly and the multilayer PCB's and each solder joint adds cost and increases the risk of corona and voltage breakdown during operation. Conventional embedded core transformers have a large number of parts and some parts require tight tolerances to facilitate precise alignment. Conventional embedded core transformers use two multilayered PCB's requiring several lamination steps and the multilayer PCB's impede vertical heat transfer away from the core assembly leading to higher operating temperatures and reduced reliability. Conventional core transformers require multiple soldering steps using a high temperature solder at solder joints between the core assembly and the PCB's and low temperature solder at solder joints between the PCB's and other components. Accordingly there is a need to simplify and improve the reliability of embedded core transformers. In particular, there is a need to reduce the number of parts and the number of solder joints in embedded core transformers.